RPM drop first while using cruise control, now randomly

octanejunkie

octanejunkie

Elite Member
Weirdest thing happened yesterday

Cruising home from the mountains with CC on doing about 70 MPH on the flats and my RPMs dropped from 2,600 to about 1,000 for a second then back up to 2,600 - the RPMs are actually dropping and the truck is bucking, it's not just the RPM gauge faltering.

It did this about 4-5 times in a few minute period so I took it out of CC and it didn't happen again.

Any thoughts?

The fact that the truck bucks makes me wanna replace my fuel pump, proactively but 23221-46010 at Camelback is $241 any cheaper than factory options here?
 
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Did your tach only indicate the loss in RPMs? Or did you actually feel the drop too?

Not saying you're wrong in your diagnosis, but I'd want to know with more certainty what the issue is before throwing money at it.
 
octanejunkie said:
Weirdest thing happened yesterday

Cruising home from the mountains with CC on doing about 70 MPH on the flats and my RPMs dropped from 2,600 to about 1,000 for a second then back up to 2,600

It did this about 4-5 times in a few minute period so I took it out of CC and it didn't happen again.

Any thoughts?

Makes me wanna replace my fuel pump, proactively - also any cheaper than factory options here?
23221-46010 at Camelback is $241
Click to expand...

My tach did that once and freaked the heck out of me. It dropped from about 2,000 to 1,000, then back up again. The engine speed did not change, just the tach. It never did it again.
 
jbrentd said:
Did your tach only indicate the loss in RPMs? Or did you actually feel the drop too?
Click to expand...

Felt the drop

gamefreakgc said:
My tach did that once and freaked the heck out of me. It dropped from about 2,000 to 1,000, then back up again. The engine speed did not change, just the tach. It never did it again.
Click to expand...

Well the truck did it again this morning when I got on the FWY, no cruise control, two slight drops/cut outs, then no issue driving the rest of the way to work (20 miles)

Fuel filter was replaced a few years ago.

I will clean the MAF sensor tonight but I don't think that's the culprit. No CEL, no codes and nothing pending.

Fuel trims (torque pro) look normal too, no big adjustments in short or long term
 
rpm drop

no codes
check connectors and resistance camshaft, cranks shaft position sensor, maf sensor, tps senor
pcv valve stuck open?
If the truck is bucking then may be a misfire.
 
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Might also start to suspect an issue with the cruise control system if it never does anything like that while you're driving it with your foot.

The engine doesn't know if the CC actuator (box over on the passenger side inner fender) is keeping the throttle open, or the gas pedal.
 
JohnMc said:
Might also start to suspect an issue with the cruise control system if it never does anything like that while you're driving it with your foot.

The engine doesn't know if the CC actuator (box over on the passenger side inner fender) is keeping the throttle open, or the gas pedal.
Click to expand...

Well the truck did it again this morning when I got on the FWY, no cruise control, two slight drops/cut outs, then no issue driving the rest of the way to work (20 miles)
 
It may also be trying to lock up the torque converter. 2600rpm in 4th the TCC I'm pretty sure is not locked.


Sent from my iPhone using Tapatalk
 
Mine used to do something pretty similar. Ended up being the wires or plug for the TPS. When it would do it, it wouldn't always throw a code but if I wiggled the harness around a little bit, it would stop for a few hundred miles. I got tired of doing that and the problem kept getting worse so I replaced about 2 feet of the harness and it stopped.
 
Doubt that it is the pump.

I would vote for TPS or IAC. My cousin drove an ES300 some years ago where it would drop the RPMs, then ultimately began dying at lights. Cleaned the plunger and chamber, which worked for some time before the solenoid gave out and a new one was the only fix.

Can you monitor the TPS values while driving?
 
Good places to start. Seems like several of us have had it happen but only sporadically.

Just to note, there's nothing wrong with your engine, since your real RPM's are not moving one bit. It has to be a bad wire/connector/sensor sending an intermittent signal that also goes to the tach.

I unfortunately don't have much to add. Mine did it the first start-up after I installed a piggyback ECU, which involved splicing and cutting many critical ECU wiring components. It never happened again but if it had, I would have just faulted it to the fact I've permanently changed the truck's wiring.

It might be the crankshaft sensor and wiring, since that was one of the major wires I cut and spliced and it's job is to send the RPM signal to the ECU (and the tach I'm guessing).
 
gamefreakgc said:
Good places to start. Seems like several of us have had it happen but only sporadically.

Just to note, there's nothing wrong with your engine, since your real RPM's are not moving one bit. It has to be a bad wire/connector/sensor sending an intermittent signal that also goes to the tach.

I unfortunately don't have much to add. Mine did it the first start-up after I installed a piggyback ECU, which involved splicing and cutting many critical ECU wiring components. It never happened again but if it had, I would have just faulted it to the fact I've permanently changed the truck's wiring.

It might be the crankshaft sensor and wiring, since that was one of the major wires I cut and spliced and it's job is to send the RPM signal to the ECU (and the tach I'm guessing).
Click to expand...

Just re-read my original post, the RPMs are actually dropping and the truck is bucking

Sorry that was not clear, editing my post now
 
I'm still a newb on 4Runners and the 3.4L V6, but I had similar symptoms as you on my old Grand Cherokee. Within a few months of each other, both the camshaft and crankshaft position sensors went out on me. The car threw codes for both and it was easy to diagnose. It would be nice if you were getting some sort of codes to help with the diagnosis.
 
I didn't clean the MAF as planned and drove with no issue today, so far

I will check all wiring connections around the TPS, IAC, cam and crank sensors, etc
 
When mine would start acting up, I could her the idle change when the wires for the tps got moved around. And the tps readings were off by a few % on my torque app.
 
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